The present disclosure relates generally to communications networks, and more particularly, to advertising alternate paths at Border Gateway Protocol (BGP) route reflectors.
For routing purposes, a network may be considered to be divided into different autonomous systems wherein each autonomous system (AS) is a group of routers under common administrative control. The routing of packets within an AS is addressed by an intradomain protocol or interior gateway protocol (IGP) operative within that AS. Routing of packets across AS boundaries is controlled by an interdomain routing protocol or Border Gateway Protocol. BGP is used to exchange routing information among network elements in the same or different autonomous system.
The distribution of BGP routing information within an autonomous system typically requires all routers to be fully meshed. In order to establish a full mesh, each BGP speaker is configured with the identities of its neighbors. A router then establishes a communication session and exchanges BGP messages to convey routing information. Establishing a full mesh constitutes a significant routing scalability challenge and an operational problem in terms of configuration management. This has led to the wide-spread use of route reflection, primarily in order to reduce the number of systems which configuration must be modified in order to introduce or remove an internal BGP speaker. Route reflectors have met with great success and have proliferated throughout the Internet.
Although route reflection can help improve routing scalability and ease the burden of configuration management, route reflection implies with it information reduction, which is not always desired. Conventional deployment of route reflectors thus has drawbacks including a lack or decrease of path diversity.
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